After cross testing with GNU/Linux, i've found out that my Intel 82577LC em(4) ethernet adapter won't do gigabit ethernet even when forced to with media options on #OpenBSD *head scratching*
@canadianbryan I know why if_em.c use auto-negociation no matter what now, thanks :)
Sorry if it wasn't clear, but the exact same setup does gigabit ethernet if the computer with the "faulty" adapter runs GNU/Linux. I tried with 3 different cables and they say the same story. Throughput also match with the media type used.
It also does gigabit on #NetBSD, and their code has special fixes for this adapter.
(They've a cool console font and green kernel messages too ^^)
And OpenBSD has these fixes but in a separate .c file. I tried to import the NetBSD's miidevs relevant entry and rebuilt miidevs.h to no avail.
I've to admit i'm punching above my weight here. But i've learnt many things in the process, like mii and mdio. Won't look at network cables the same way now ^__^
@julianaito auto-neg is mandatory for GigE, if it's not working it's likely a cable issue.